The sea lamprey (Petromyzone marinus) is the only modern survivor of an ancient family of "jawless" fishes that dates back almost 250 million years. These eel-like creatures were originally a salt water ocean fish, migrating into fresh water streams only to spawn. However, when in the early 1900's the United States and Canadian Great Lakes (Lakes Superior, Michigan, Huron, Erie and Ontario) were made accessible to the Atlantic Ocean by way of man-made canals, sea lampreys migrated into each of the lakes over a course of years, eventually completley their full life cycle in fresh water.
In the adult phase of the life cycle, the lamprey has an eel-like body with a large downward-slanting mouth at one end. The mouth is equipped with sucking discs with which the lamprey attaches to prey, usually other fish such as salmon and perch, and feeds on blood and other body tissue. The sea lamprey has, for many years now, been a source of major concern for those involved in the Great Lakes fishery. Due, at least in part, to the lamprey invasion, the fish harvest in the Great Lakes declined drastically in the first half of the 1900's.
Various methods of lamprey control have been employed with varying degrees of success. One of those methods involved erecting barriers to deny the lamprey access to spawning areas. That method proved to be costly to build and maintian and also commonly proved ineffective when lampreys found alternate spawning areas.
A further method involved adding an electrical current to the barriers to shock the lampreys when they approached. This method also had disadvantages in that it was expensive to operate, to a large degree inefective and sometimes had the undesirable effect of killing other fish.
The main method of lamprey control that has met with some success is through the release of chemicals containing a compound specifically deadly to lamprey larvae into the water systems. While this method has proved to be more effective than those discussed above, there are continuing concerns about the introduction of foreign chemicals into the water sytems. Certain other fish and insect species have been affected. Also, chemical treatment has been less than 100% effective. Lamprey numbers continue to be a concern in each of the Great Lakes and in many of the connecting rivers and streams.
The present invention has several advantages over the prior methods described above. The method is simple and will be effective is strongly curtailing if not eliminating lamprey numbers where it is practised. The method will be relatively inexpensive as very little ongoing maintenance will be required. The method of this invention will also involve no use of chemicals or the introduction of any other foreign matter into the water system.